A spent nuclear fuel assembly having burnt at the end of a nuclear fuel cycle is referred to as “recycle fuel”. Since the recycle fuel contains highly radioactive materials such as FPs and needs to be thermally cooled, it is cooled in a cooling pit in a nuclear power plant for a predetermined period of time. The cooled recycle fuel is then contained in a cask, which is a shielding container, and the cask is transported and stored in reprocessing facilities or intermediate storage facilities by truck, ship or the like.
If the cask is transported to the reprocessing or intermediate storage facilities, the recycle fuel containing highly radioactive materials is contained in the cask. Therefore, the cask should be kept shielded and hermetically sealed as much as possible unless it is unnecessary to do so. To do so, during transport of the cask, the cask is protected by covering both ends of a cask main body with cask buffer bodies. By doing so, even if the cask falls, for example, the cask is kept shielded and hermetically sealed. As an example of the cask buffer body of this type, Patent Document 1 discloses a cask buffer body having an interior filled with a wood material.    Patent Document 1: Japanese Patent Application Laid-open No. 2003-315493.